Gray cast iron



Ratented Feb. 20, 1951 can css'r mom AlbertlaulGsgnebmltedBanhandWu-renlilcLellan Spear, Elisabeth, N. 3., alsignon to The International NickelCompany, Inc New York, N. Y., a corporation of Delaware No Drawing.Application September 11, ms,

Serial 110.116.421

1'. Claims. (01. 75-123).

The present invention relates to a novel method for the production 01gray cast iron containoccurrence of graphite in a spheroidal form.

Generally speaking, the present invention contemplates a novel processfor producing hypoeutectic gray cast iron containing uncombined carbonor graphite in a substantially spheroidal form in the as-castconditionand the product produced thereby. The novel process contemplated by thepresent invention comprises incorporating in a molten iron bath havingsuch a, composition as to be a. hypoeutectic gray castiron wheninoculated and cast an amount of magnesium suflicient to provide aretained magnesium content of at least about 0.015% but less than about0.035% or 0.04% in castings made from said bath, an amount of ceriumsumclent to provide a retained cerium content of at least about 0.015%and up to about 0.16% in castings made from said bath with a totalcontent of magnesium and cerium in said castings being at least about0.035% or 0.04% up to about 0.2% and casting metal from said treatedbath in an inoculated condition to produce castings of hypoeutectic castiron containing uncombined carbon or graphite in a spheroidal form inthe ascast condition. Very satisfactory results are obtained when theretained content of magnesium plus cerium is about 0.05% to about0.075%, 1.

- though retained contents of magnesium plus cerium of up to about 0.1%can be employed especially in compositions having high graphitizingpower, e. g., those cast in heavy sections such as about four inches.The cerium content is usually less than about 0.1%, e. up to 0.06% or0.08

As those skilled in the art know, cast irons are eutectiierous alloyswhose principal constituents are iron and carbon and hypoeutectic castirons I are those containing lesscarbon than the eutectic amount. Theeutectic amount of carbon in any particular composition variesdependingupon the amounts of other elements in the composition, e. g.,silicon. Hypoeutectic gray cast irons are those containing carbon,silicon and phosphorus in such amounts that the carbon content plusone-third the silicon content plus one-third the phosphoru content isless than 4.3, e. g., 4.2 or less, with the carbon in excess of thatrequired to form the matrix being predominantly in the uncombined form.In general, the gray cast iron compositions produced according to thepresent invention contain, in addition to the aforesaid amounts ofmagnesium and cerium, about 1.7% to about 3.9% carbon with the excesscarbon not required to form the matrix being predominantly uncombined,about 1.2% to about 7% silicon, about 0.05% to about 2% manganese, up toabout 0.5% phosphorus, up to'about 10% nickel, e. g., about 0.05% toabout 3% nickel, up to about 2% copper, e. g... about 0.05% to about1.5% copper, and the balance essentially iron to provide a ferrousmatrix. The iron content is usually at, least about 85% or 80% ofthetotal composition and the iron is in the alpha form at atmospherictemperatures. Th carbon content in castings produced in accordance withthe invention is controlled such that it is always less than the valuerepresented by the formula 4.3 minus 5 (Si+P). Particularly satisfactoryresults are obtained when the carbon content is about 2.5% to about 3.7%and the silicon content is about 1.5% to about 3%. Such castings usuallycontain at'least about 1.3% or 1.5% uncombined carbon or usually about2% uncombined carbon in the as-cast condition.

Within. the ranges of composition set forth hereinbeiore, the retainedmagnesium and cerium contents contemplated by the invention cooperate toproduce a new result, 1. e., the production 01' 'a hypoeutectic graycast iron containing graphite or uncombined carbon in a spheroidal formalthough the retained magnesium content is insumcient by itself tocontrol the occurrence of a large proportion 01' the graphite in aspheroidal form. This result is unexpected in view of the fact thatcerium, in the absence of magnesium, is not eil'ective by itself inhypoeutectic cast iron compositions to provide the results obtained bythe present invention but acts as a desulfurizer and carbide stabilizeror whitener even when inoculation is employed after the introduction ofcerium.

In the process contemplated by the invention for producing spheroidalgraphite in a hypoeutectic gray cast iron composition, inoculation is anessential feature required to produce uncombined carbon or graphite inthe solidified product provided by the invention. Inoculation of thehypoeutectic cast iron bath is accomplished along with or subsequent tothe incorporation therein of the amounts of magnesium and ceriumcontemplated by the invention. Inoculation is accomplished by a lateaddition of an inoculant, e. g., silicon. Preferably, the graphitlzinginoculation is carried out after the incorporation of magnesium andcerium into the molten hypoeutectic cast iron bath. Very satisfactoryresults have been obtained using ferrosilicon, e. g., an iron alloycontaining a major proportion up to about 95% silicon as the inoculatingagent although other metallic silicon-containing agents or alloys, suchas nickel-silicon alloys' or nickel silicide, calcium-silicon alloys orcalcium silicide, silicon metal and various proprietary inoculatingalloys commonly used for reducing, dendriticism and reducing chill infoundry gray cast irons may be employed. As those skilled in the artknow, commercially available ferro-silicon and various proprietaryinoculants usually contain calcium, e. g., up to about 1% or so, and thepresence of this element has been recognized to increase theefiectiveness of the inoculant in many instances. It is also known thatferrosilicon and various proprietary inoculants often contain aluminum.It is preferred to employ silicon in amounts between about 0.3% andabout 2% or 2.5%, more preferably between about 0.4% and about 1.2%, asthe late addition to effect inoculation. Since the aforesaid amounts ofsilicon are added to effect inoculation in the process embodying thepresent invention, the initial silicon content of the hypoeutectic castiron bath to be treated in accordance with the present invention isusually about 0.8% to about 2%.

In carrying out the process contemplated by the invention to producehypoeutectic gray cast iron containing spheroidal carbon and having highductility, it is preferred that the manganese content be low as thiselement detrimentally affects the ductility. Thus, it is preferred thatthe manganese content not exceed about 0.3% to provide good ductility.When high strength, rigidity and wear resistance are desired, apearlitic matrix containing about 0.5% to about 0.9% manganese isemployed. Phosphorus, which is usually considered an impurity but whichin the usual amounts does not materially interfere with the formation ofspheroidal graphite, is also preferably maintained at a low level asphosphorus detrimentaliy affects the ductility. Although the phosphoruscontent may be as high as about 0.5% or more,- phosphorus preferablydoes not exceed approximately 0.25% and more preferably does not exceedabout 0.1%. The sulfur content in hypoeutectic cast iron productsproduced in accordance with the invention is low, usually not exceedingabout 0.02% e. g., about 0.01% to about 0.018%. Certain other elementsnot usually found in cast iron should be avoided or should be presentonly in traces or in very small amounts because these elements interferewith the formation of spheroidal graphite. These subversive elementsinclude tin, lead, antimony, bismuth, arsenic, selenium, tellurium, etc.These elements preferably are not present in a total amount over about0.05%. Other alloying elements which may be present in the compositionto provide specific effects upon the matrix structure include up toabout 1% chromium, up to about 1% molybdenum, up to about 0.5% vanadium,etc.

Magnesium can be introduced into' the molten hypoeutectic gray 'castironin metallic form provided proper precautions are observed or it canbe introduced in the form of an alloy. Nickel, copper and/or silicon arethe preferred metals with which magnesium is alloyed to form an additionagent's; Very satisfactory alloys inum-carbon alloys containing about10% to about 15% magnesium, and about 1.5% to about 3% carbon;nickei-magnesium-silicon alloys containing about 13% to about 20%magnesium and about 20% to about 30% silicon; and iron-magnesium-siliconalloys containing about 12% to about 16% magnesium and about 30% toabout 60% silicon. Cerium is added to the molten cast iron in the formofcerium metal or as an alloy or a mixture, e. g., mischmetal.

In carrying out the process contemplated by the invention, particularlywhen the sulfur content of the hypoeutectic cast iron bath to be treatedis about 0.05% or 0.06% to 0.15% or more, e. g., up to about 0.3%sulfur, magnesium in an amount suflicient to reduce the sulfur contentof the bath, e. g., to a value below about 0.03% or 0.02%, and toprovide the required retained magnesium content in castings made fromthe bath is incorporated in the bath; thereafter the required amounts ofcerium are incorporated in the bath, the bath is inoculated at leastonce and metal from this treated inoculated bath is cast to obtainhypoeutectic gray cast iron containing spheroidal graphite.Alternatively, other means may be used to reduce the sulfur below about0.05% or even below about 0.02% prior to the introduction of magnesiumand/or 'cerium, e. g., by means of a basic slag, etc., and

this practice is beneficial and advantageous. When the sulfur content ofthe hypoeutectic cast iron bath is low, e. g.. below about 0.05%, thecerium addition can be made simultaneously with the magnesium addition,or even prior thereto. Magnesium isa very powerful dasulfurizer in castiron baths, even baths which are held under acid conditions, as in anacid-lined ladle, etc. About one part by weight of magnesium isintroduced into the cast iron bath for each part by weight of sulfur tobe removed and the magnesium consumed in removing sulfur is noteffective to promote the formation of graphite in a spheroidal form. Ofcourse,.suflicient magnesium must be added not only to compensate forthe losses of magnesiumencountered in removing sulfur from the cast ironbath, in the addition reactions, in holding the bath after theincorporation of magnesium, etc., but

also to incorporate the required amounts of mag-- cerium in the castiron bath to provide the reauacss quired retained cerium content in thefinal casting In the novel gray cast iron product provided by theinvention in the as-cast condition. some or practically all of the,uncomblned carbon or graphite appears as compact, soft, gray-colored,rounded particles or spheroids, or as agglomerates or groups of suchparticles. These rounded particles or spheroids of uncomblned carbon orgraphite visible in properly polished and etched sections have awell-defined radial or radiating structure. The particle has theappearance of a plurality of crystals radiating from approximately thecenter, i. e., a radiating and polycrystalline appearance. At leastsome, e. g., usually about or more, ofthe uncomblned carbon or graphiteis in a spheroidal form in the novel gray cast iron provided by theinvention. When some of the uncomblned carbon or graphite is in thespheroidal form, the use of a slightly higher amount of retainedmagnesium and/or cerium, e. g., about 0.01% or 0.02% additional retainedmagnesium and/or cerium, is sufiicient in most cases to cause theuncombined carbon or graphite to appear predominantly in a substantiallyspheroidal form.

The novel product provided by the invention containing spheroidalgraphite in the as-cast condition possesses a very remarkablecombination of properties and characteristics. In genveral, the tensilestrength of the as-cast product and drawing, normalizing and drawing.austempering, annealing at temperatures both above and/or below thecritical temperature, slow cooling from the casting temperature, etc.

For the purpose of giving those skilled in the art a betterunderstanding of the invention, the following illustrative examples aregiven:

Example 1 A hypoeutectic cast iron bath containing about 2.8% carbon,about 1.5% silicon, about 0.06% manganese, and about 0.07% phosphoruswas established. To one portion of the bath, sufiicient magnesium wasincorporated to provide a retained, magnesium content of about 0.016%,and

sufficient cerium was incorporated to providea retained cerium contentof about 0.031% in the final casting. The treated metal was inoculatedwith about 0.5% silicon as ferrosilicon and cast. This casting, made inaccordance with the present invention, was a gray cast iron, hadgraphite.

oculated with about 0.5% silicon as commercial will be 50% ormoregreater than would be obtained in the same composition devoid ofmagnesium, and usually the improvement in tensile strength will be 100%or much more. Tensile strengths on the order of 85,000 pounds per squareinch or more are obtained in the pearlitic (i. e., generally preferred)compositions. The

high tensile strengths are obtained in combinaemit a definite steel-likering rather than the duller sound emitted by gray cast iron. A highlyuseful property possessed by castings manufactured in accordance withthe invention is that the hardness within a particular casting is veryuniform even though the section size of the casting varies considerably.

As indicated hereinbefore, the generally preferred matrix structure inthe-as-cast product provided by the invention is a pearlitic matrix.However. the spheroidal form of uncomblned car.- bon or graphite whichcharacterizes the novel ascast product provided by the invention can beobtained in any matrix obtainable in gray cast irons of similarcomposition. Thus, the ferrous matrix may be pearlite, ferrite,martensite. an acicular constituent (e. g., bainite or othertransformation products of austenite explained by the 8- curve), etc.,or the known combinations thereof. When it is desired to enhance certainproperties or to modify the combination of properties, the

as-cast alloy may be subjected to known heat treatments, surfacetreatments, etc., for stress relief, hardening, strengthening,toughening, etc. Illustrative heat treatments include quenchingferrosilicon and cast. This casting. not made according to theinvention, was a. white cast iron and had a transverse load of 5700pounds, animpact value of 24, and a Brinell hardness of 430. Thefracture of this casting was white.

Example 2 A hypoeutectic cast iron melt containing about 3.3% carbon,about 1.8% silicon, about 0.6% manganese, about 0.05% phosphorus, andabout 0.03% sulfur was established. To one portion of the bath,sufiicient magnesium was incorporated to provide a retained magnesiumcontent of 0.014%, and sufiicient cerium was incorporated to provide afinal retained cerium content of about 0.016% in the final casting, i.e., the final casting had a magnesium plus cerium content of about0.03%. The treated metal was inoculated with about 0.5% silicon ascommercial ferrosilicon and cast. This casting, not made according tothe invention, had a gray fracture and, when tested under the sameconditions as in Example 1, had a transverse load of about 3480 pounds,impact value of about 29, and a Brinell hardness of about 179. Intoanother portion of the aforesaid bath, sufiicient cerium to provide afinal retained cerium content of about 0.019% and sufficient magnesiumto provide a fiIlltl retained magnesium content of about 0.016% wereincorporated, i. e., the final casting had a magnesium plus ceriumcontent of about 0.035%. This portion was likewise inoculated with about0.5% silicon as commercial ferrosilicon and cast. This casting, made inaccordance with the invention, was a gray cast iron containing asubstantial portion of the graphite as spheroids. The fracture of thiscasting'was steely, and, when tested 7 casting had a magnesium pluscerium content of about 0.05%. The thus-treated metal was inoculatedwith about 0.5% silicon as commercial ferrosilicon and cast. Theresulting casting, made in accordance with the invention, was a graycast iron containing substantially all the graphite as spheroids. Thefracture of the casting was steely and, when tested under the sameconditions as Example 1, the casting had a transverse strength of about8770 pounds, an impact value greater than 120. and a Brinell hardness ofabout 268.

It is recognized that magnesium and cerium determinations of the orderinvolved herein are difllcult to make. The values given herein for theseelements are based upon analyses-which have been checked and arereproducible within about 0.005% and the values given for cerium arereproducible within about 10%.

The present invention may be applied to the manufacture of a widevariety of ferrous prod- 8 made from said bath and sumcient cerium toprovide a retained cerium content ofat least about 0.015% in castingsmade from said bath, inoculating said bath with about 0.3% to about 2.5%silicon and casting the metal from the inoculated bath in an inoculatedcondition to obtain a hypoeutectlc gray iron casting containing about0.05% to about 0.075% magnesium plus cerium and containing graphite in asubstantially spheroidal form.

2. The improved process for producing hypoeutectic gray cast ironcontaining spheroidal nets and articles. For example, enginecrankshafts, machinery parts such as roll mill houslugs and run-outtables for steel mill equipment, ingot molds, railroad castings, marinecastings, castings for agricultural implements, automotive castings,etc., can be made of the alloy provided by the invention. 7

It is to be noted that the present invention is not to be confused withthe teachings and disclosures of Morrogh et al. (for example, in thearticle published in the March 1948 issue of the Journal of the Iron andSteel Institute at pages 306 et seq., in the article published in theApril 1948 issue of American Foundryman at pages 91 et seq., etc.) sincethe cerium treatment process disclosed by Morrogh et al. must be appliedto a 'hypereutectic cast iron composition and is aptic cast irons arenot commonly used in commercial practice. The present process, on theother hand, is applied specifically to the treatment of hypoeutecticcast iron melts more commonly employed in commercial practice and is notrestricted to the treatment of cast iron melts of very low sulfurcontent.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will understand. Suchmodifications and variations are considered to be within the purview andscope of the invention and of the appended claims.

We claim:

l. The improved process for producing hypoeutectic gray cast ironcontaining spheroidal graphite which comprises establishing an iron bathhaving such a composition as to be a hypoeutectic gray cast iron wheninoculated and cast, incorporating in said bath sufllcient magnesium toprovide a retained magnesium content of at least about 0.015% but lessthan about 0.04% and insumcient by itself to control the occurrence ofsubstantially spheroidal graphite in castings graphite which comprisesestablishing an iron bath having such a composition as to be ahypoeutectic gray cast iron when inoculated and cast, incorporating insaid bath sufllcient magnesium to provide a retained magnesium contentof at least about 0.015% to about 0.035% and insuflicient by itself tocontrol the occurrence of substantially spheroidal graphite incastingsmadefrom said bath and sufncient cerium to provide a retained ceriumcontent of at least about 0.015% in castings made from said bath; andcasting the metal from the bath in an inoculated condition to obtain ahypoeutectic iron casting containing about 0.035% to about 0.1%magnesium plus cerium and containing graphite in a substantiallyspheroidal form in the as-cast condition.

3. The improved process for producing hypocast iron bath having such acomposition as to be a hypoeutectic gray cast iron bath when cast' in aninoculated condition, incorporating in said bath an amount of magnesiumsuillcient to provide a retained magnesium content of at least about0.015% but less than about 0.04% and insunlcient by itself to controlthe occurrence of a substantial amount of graphite in a substantiallyspheroidal form in castings made from said bath and an amount of ceriumsuilicient to provide a retained cerium content of at least about 0.015%to'about 0.1% in castings made from said bath, and casting metal fromthe thus-treated bath to obtain hypoeutectic gray cast iron castingscontaining a substantial amount of graphite in a substantiallyspheroidal form and characterized by an improved combination ofproperties as compared to the properties of a similar gray iron castingnot containing both magnesium and cerium in the aforesaid amounts.

4. The improved process for producing hypoeutectic gray cast ironcontaining uncombined carbon in a substantially spheroidal form whichcomprises incorporating ina molten cast iron bath having such acomposition as to be a hypoeutectic gray cast iron bath when cast'in aninoculated condition an amount of magnesium suillcient to provide aretained magnesium content of at least about 0.015% but'less than, about0.04% and insufllcient by itself to control the occurrence of asubstantial amount of uncombined carbon in a spheroidal form incastingsmade from said bath and an amount of cerium ,suificient to provide aretained cerium content of at least about 0.015% but less than about0.16% in castings made from said bath, and castings containing asubstantial amount of the uncombined carbon in a substantiallyspheroidal form and characterized by an improved combination ofproperties as compared to the properamass 0.015% cerium, the sum of theretained magnesium and retained cerium contents being at least about0.035%. and casting metal from said bath containing the aforesaidamounts of magresium and cerium in an inoculated condition to obtain ahypoeutectic gray cast iron casting containing phite in a substantiallyspheroidal form and having an improved combination of properties ascompared to a similar casting devoid of magnesium.

6. The process for producing an improved hypoeutectic gray cast ironwhich comprises establishing a bath of molten iron or such a comaposition as to be a hypoeutectic gray cast iron when inoculated and castand containing over about 0.06% sulfur, reducing the sulfur content to avalue less than about 0.05%, incorporating into said bath 'an amount ofmagnesium sufficient to provide a retained magnesium content of at leastabout 0.015% to about 0.035% and insufllcient by itself to control theoccurrence of graphite in aspheroidal form in castings made from saidbath, incorporating into said bath an amount of cerium suflicient toprovide a retained cerium content of at least about 0.015% up to about0.08% in castings made from said bath, inoculating said bath with about0.3% to about 2.5% silicon and casting metal from said bath in aninoculated condition to obtain a hymeutectic gray cast iron castingcontaining raphite in a spheroidal form and containing at least about0.035% magnesium plus cerium.

7. The process for producing an improved ductile hypoeutectic gray castiron whch comprises establishing a bath of molten iron of such acomposition as to be a hypoeutectic gray cast iron when cast in aninoculated conditionand containing more than about 0.08% su fur,incorporating into said bath an amount of magnesium sumcient to reducethe sulfur content thereof below about 0.03% and to provide a retainedmagnesium content of at least about 0.015% up to about 0.04% in castingsmade from said bath, incorporating into said magnesium-treated bath anamount of cerium suflicient to provide a retained cerium content of atleast about 0.015% up to about 0.1 in castings made from said bath, andcasting metal from said bath in an inoculated condition to obtain ahypoeutectic gray cast iron casting containing unccmbined carbon in aspheroidal form, and containing at least about 0.04% magnesium pluscerium.

8. An iron casting containing about 2.5% to about 3.7% carbon, with theexcess carbon not required to form the matrix being predominantlyunccmbined, about 1.5% to about 3% silicon, up to about 0.5% phosphorus,the carbon, silicon and phosphorus contents being so reated that the sumof the carbon content plus one-third the silicon content plus one-thirdthe phosphorus content is less than 4.3,-magnesium from about to controlthe occurrenceof a substant'al amount of graphite in a spheroidal form,at least about 0.015% cerium, with the um plus cerium 75 predominantlyin an unccmbined form, at least .10 content being about 0.05% to about0.075% to control the occurrence of a substantial amount of theunccmbined carbon in a substantially spheroidal form, and the balanceessentially iron to provide a ferrous matrix in which the substantiallyspheroidal unccmbined carbon particles are dispersed.

9. A hypoeutectic gray iron casting containing about 2.5% to about 3.7%carbon, about 1.5% to about 3% silicon, magnesium from about 0.015%-toless than about 0.04% and insufllcient by itself to control theoccurrence of graphite in a spheroidal form in the casting, at leastabout 0.015% cerium, with the total quantity of magnesium plus ceriumbeing about 0.04% to about 0.1% to control the occurrence of graphite ina spheroidal form, and the balance essentially iron.

10. A gray iron casting containing about 1.7% to about 3.9% carbon, withthe excess carbon not required to form the matrix being predominantlyunccmbined, about 1.2% to about 7% silicon, up to about 0.5% phosphorus,with the carbon, silicon and phosphorus contents being so related thatthe carbon content plus one-third the sificon content plus one-third thephosphorus content is less than 4.3, up to about 10% nickel, up to about2% copper, at least about 0.015% but less than about 0.04% magnesium, atleast about 0.015% cerium, with the sum of the magnesium and ceriumcontents being about 0.05% to about 0.075%, and the balance essentiallyiron, said casting being characterized by unccmbined carbon in asubstantially spheroidal form and by an improved combination ofproperties as compared to those of a similar-casting devoid ofmagnesium.

11. A gray iron casting containing about 1.7%

to about 3.9% carbon, with the excess carbon not required to form thematrix being predominantly unccmbined, about 1.2% to about 7% silicon,up to about 0.5% phosphorus, with the carbon, silicon and phosphoruscontents being so related that the carbon content plus one-third thesilicon content plus one-third the phosphorus content is less than 4.3,up to about 10% nickel, up to about 2% copper, at least about 0.015% toabout 0.04% magnesium, at least about 0.015% cerium, with the sum of themagnesium and cerium contents being about 0.035% to about 0.1%, and thebalance essentially iron, said casting being characterized by uncombinedcarbon in a substantially spheroidal form and by an improved combinationof properties as compared to those of a similar casting'devoid ofmagnesium.

12. A gray iron casting containing magnes um from about 0.015% to about0.035% and insufllcient by itself to control the occurrence of graphitein a spheroidal form in the casting and at least about 0.015% cerium,with the total quantity of magnesium plus cerium being about 0.035% toabout 0.1% tocontrol the occurrence 'of graphite in a substant allyspheroidal form,

with the balance being a hypoeutectic cast iron composition.

13. An iron casting containing at least about 0.015% up to about 0.04%magnesium, at least about 0.015% and up to about 0.16% cerium, with thetotal quantity of magnesium plus cerium being about 0.04% to about 0.2%,and containng unccmbined carbon in a substantially spheroidal form withthe balance being a hypoeutectic gray cast iron composition.

14. An improved gray iron casting containing the carbon not required toform the matrix about 0.015% up to about 0.06% cerium, a small buteiiective amount up to about 0.035% of ma:- nesium insumcient by itselfto control the occurrence of unoombined carbon in a spheroidal form insaid casting but eiiective in combination with the aforesaid amounts ofcerium to control the occurrence of uncombined carbon in a spheroidalform in said casting. and. the balance a hypoeutectic cast ironcomposition devoid of subversive amounts of elements which materiallyinterfere m with the formation 01' uncombined carbon in a 12 numlmcascrrm The ioliowing references are of record in the iiie of um patent:

UNI-ran s'ra'rae rsm're Number Name Date 2,485,760 Millie et a1 Oct. 25,1949 2,485,781 Millie et al. Oct. 25, 1040 2,488,511 Morroch Nov. 15,190

1. THE IMPROVED PROCESS FOR PRODUCING HYPOEUTECTIC GRAY CAST IRONCONTAINING SPHEROIDAL GRAPITE WHICH COMPRISES ESTABLISHING AN IRON BATHHAVING SUCH A COMPOSITION ESTABLISHING AN IRON EUTECTIC GRAY CAST IRONWHEN INOCULATED AND CAST, INCORPORATING IN SAID BATH SUFFICIENTMAGNESIUM TO PROVIDE A RETAINED MAGNESIUM CONTENT OF AT LEAST ABOUT0.015% BUT LESS THAN ABOUT 0.04% AND INSUFFICIENT BY ITSELF TO CONTROLTHE OCCURRENCE OF SUBSTANTIALLY SPHEROIDOL GRAPHIC IN CASTINGS MADE FROMSAID BATH AND SUFFICIENT CERTIUM TO PROVIDE A RETAINED CERIUM CONTENT OFAT LEAST ABOUT 0.015% IN CASTING MADE FROM SAID BATH, INOCULTING SAIDBATH WITH ABOUT 0.3% TO ABOUT 2.5% SILICON AND CASTING THE METAL FROMTHE INOCULATED BATH IN AN INOCULATED CONDITION TO OBTAIN A HYPOEUTECTICGRAY IRON CASTING CONTAINING ABOUT 0.005% TO ABOUT 0.075% MAGNESIUM PLUSCERIUM AND CONTAINING GRAPHIC IN A SUBSTANTIALLY SPHEROIDAL FORM.
 8. ANIRON CASTING CONTAINING ABOUT 2.5% TO ABOUT 3.7% CARBON, WITH THE EXCESSCARBON NOT REQUIRED TO FORM THE MATRIX BEING PREDOMINANTLY UNCOMBINED,ABOUT 1.5% TO ABOUT 3% SILICON, UP TO ABOUT 0.5% PHOSPHORUS, THE CARBON,SILCON AND PHOSPHORUS CONTENTS BEING SO RELATED THAT THE SUM OF THECARBON CONTENT PLUS ONE-THIRD THE SILICON CONTENT PLUS ONE-THIRD THEPHOSPHORUS CONTENT IS LESS THAN 4.3, MAGNESIUM FROM ABOUT 0.015% TOABOUT 0.035% AND UNSIFFICIENT BY ITSELF TO CONTROL THE OCCURRENCE OF ASUBSTANTIAL AMOUNT OF GRAPHIC IN A SPHEROIDAL FORM, AT LEAST ABOUT0.015% CERIUM, WITH THE MAGNESIUM PLUS CERIUM CONTENT BEING ABOUT 0.05%TO ABOUT 0.75% TO CONTROL THE OCCURRENCE OF A SUBSTANTIAL AMOUNT OF THEUNCOMBINED CARBON IN A SUBSTANTIALLY SPHEROIDAL FORM, AND THE BALANCEESSENTIALLY IRON TO PROVIDE A FERROUS MATRIX IN WHICH THE SUBSTANTIALLYSPHEROIDAL UNCOMBINED CARBON PARTICLES ARE DISPERSED.